For the biological hydroxylation of steroids at the 25-position, there is already known a process wherein microorganisms of the genus Streptomyces capable of hydroxylating steroids at the 25-position thereof are used [Japanese Patent Unexamined Published Application (hereinafter referred to as "J. P. KOKAI") No. Hei 7-123997]. Concretely, Streptomyces sp. HB-103 is mentioned therein as the microorganisms of the genus Streptomyces. With this kind of microorganisms, steroids having complicated structures can be efficiently, easily and directly hydroxylated at the 25-position.